JPH11299107A - Controller for self-excited converter and direct-current transmission equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to transmit a direct current without interruption even in case of an alternating-current system failure on the separately excited converter side, by, if the voltage is lower than a rated direct-current voltage, setting and controlling the direct-current voltage of a self-excited converter according to the magnitude of the alternating-current voltage of the separately excited converter. SOLUTION: The controller for a self-excited converter is provided with a constant-voltage control circuit which controls the direct-current voltage of a direct-current transmission equipment to a rated value, and exercises constant-voltage control using a direct-current voltage command value and a voltage value acquired from a direct current transformer. Also, the controller acquires the input-side alternating-current voltage of a separately excited converter and performs current controlling operation under predetermined conditions. The constant-voltage control AVR2 operates when a direct current set value is between a lower limit current command value Idl, and an upper limit current command value Idu, with a current command value Idr intervening therebetween. Below the lower limit current command value Idl, a current characteristic wherein the current set value varies depending on the direct-current voltage is provided, and a current command value Idp=(Idl/Vdr)×Vdf is created from a direct-current voltage detection value Vdf.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC power transmission equipment for converting an AC into a DC and transmitting the power, and converting the AC to an AC again at a load site, and a control device therefor. The present invention relates to a hybrid DC power transmission facility including a converter and a control device for a self-excited converter.

[0002]

2. Description of the Related Art Self-commutated converters are being developed for application to DC power transmission. The self-excited converter can perform power conversion without being affected by the AC system, and can arbitrarily and quickly control the reactive power from advance to delay.

[0003] According to the study of the present inventors, a self-excited converter is used as an invertor that can take advantage of the above-mentioned application merits.
On the other hand, using a separately-excited converter that is advantageous in terms of manufacturing cost and element withstand voltage for the forward converter, it is expected that hybrid DC transmission equipment with a configuration combining the separately-excited converter and the self-excited converter will be used in the future. Promising. In this case, the self-excited converter (inverter side) performs a constant voltage control operation to keep the DC circuit voltage constant from the main circuit configuration, and the separately-excited converter (forward converter side) specifies the transmission power. It is convenient to adopt an operation system in which constant current control (constant power control) operation is performed to keep the value of.

[0004]

However, when the above-mentioned operation method is adopted, an accident occurs in the AC system on the side of the forward converter, and the AC voltage decreases, so that the DC voltage of the forward converter cannot exceed the rated value. Otherwise, the DC voltage on the inverter side becomes higher than that on the forward converter side, so that current cannot flow through the inverter. For this reason, there is a problem that DC transmission stops.

On the other hand, in the reverse converter, since the inflow of power from the forward converter is stopped, the power to be converted to the AC side is reduced to prevent the DC voltage from lowering and to perform the operation of keeping the DC voltage constant.

[0006] As described above, the fact that the DC power transmission may be stopped due to the AC system fault on the forward converter side is an obstacle to the practical use of the hybrid DC power transmission equipment.

[0007] The present invention provides a DC power transmission facility comprising a combination of a self-excited converter and a separately-excited converter, which can perform DC power transmission without stopping even in the event of an AC system fault on the forward converter side.
It is another object of the present invention to provide a control device for a self-excited converter.

[0008]

According to a first aspect of the present invention, a separately-excited converter and a self-excited converter are connected to each other via a DC circuit. In the control device of the self-excited converter in DC power transmission equipment,
At a voltage lower than the rated DC voltage, the DC current of the self-excited converter is set according to the magnitude of the AC voltage of the separately-excited converter, and has a current control characteristic of controlling to the set current value. A control device for a self-excited converter is provided.

According to a second aspect of the present invention, in a control device for a self-excited converter of a DC power transmission facility configured by connecting a separately-excited converter and a self-excited converter via a DC circuit, Provided is a control device for a self-excited converter, characterized in that the DC current of the self-excited converter changes according to the magnitude of the DC voltage of the self-excited converter at a voltage lower than the DC voltage.

[0010] According to the third aspect of the present invention, in a DC power transmission facility configured by connecting a separately-excited converter and a self-excited converter via a DC circuit, the magnitude of the AC voltage of the separately-excited converter is increased. DC transmission equipment, comprising: a detection unit for detecting the voltage, a transmission line for transmitting the detected voltage value, and a control device for the self-excited converter according to the first aspect. Provided.

According to a fourth aspect of the present invention, in a control device for a self-excited converter for converting a DC current transmitted under constant current control into an AC, the voltage of the transmitted DC current is determined in advance. When the input side voltage is equal to or more than the predetermined threshold, the input side voltage is controlled by a constant voltage, and when the voltage of the transmitted DC current is less than the threshold, the input side voltage is set to a predetermined current value according to the DC current voltage. A control device for a self-excited converter characterized by controlling a current is provided.

According to a fifth aspect of the present invention, in a hybrid DC power transmission facility configured by connecting a separately-excited converter and a self-excited converter via a DC circuit, the converter is supplied to the separately-excited converter. A detection unit for detecting power, a transmission line for transmitting the detected power value, and an input-side voltage that is constant when the voltage of the transmitted DC current is equal to or higher than a predetermined threshold. Voltage control, if the voltage of the transmitted DC current is less than the threshold value, a self-excited converter for controlling the input side current to a predetermined current value according to the value of the transmitted power A DC power transmission facility comprising a control device is provided.

According to a sixth aspect of the present invention, in a control device for a self-excited converter connected to an operation command device for converting a DC current transmitted under constant current control into an AC, the operation command device From the DC voltage command value Vdr, the predetermined upper limit value Idu of the effective current command value, and the DC voltage detection value Vdfr of the DC current to be transmitted, to create an effective current command value corresponding to the DC voltage. , A first constant power control circuit for controlling the active power when the self-excited converter operates in the forward converter to the command value Pdr, and a DC voltage of the self-excited converter specified value. Vdr
A constant voltage control circuit, a second constant power control circuit for controlling the active power when the self-excited converter performs the inverse converter operation to the command value Pdi, the current command value creation circuit, A signal selection circuit for selecting an output from the constant power control circuit, the constant voltage control circuit, and the second constant power control circuit according to an operation state of the self-excited converter; and a self-excited converter. A reactive power control circuit for controlling the reactive power on the AC side to become a reactive power command value Qr from the operation command device; and a self-excited converter for converting the active current command value selected by the signal selection circuit into a command value. An active current control circuit for controlling an active component of the AC current, and a reactive current control circuit for controlling the reactive component of the AC current of the self-excited converter to a reactive current command value specified by the reactive power control circuit. The output of the effective current control circuit, and , For converting two outputs of the output of the reactive current control circuit of bi-signal to the 3-phase signal 2 [phi / 3
φ conversion circuit and PWM for generating a pulse signal for controlling a self-excited converter from the signal converted into the three-phase signal
A pulse generator circuit, wherein the first and second constant power control circuits set a small current value in accordance with a drop from a rated value of the DC current, and control the self-excited converter. An apparatus is provided.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

First, with reference to FIG. 3, one embodiment of a hybrid DC power transmission facility including a separately-excited converter and a self-excited converter to which the present invention is applied will be described. The hybrid DC power transmission equipment in the present embodiment is basically configured in the same manner as the conventional hybrid DC power transmission equipment, but mainly includes the control content of the self-excited converter (inverter side) and the separately-excited conversion. Container (forward converter side)
In that an AC voltage transformer for detecting the AC voltage is provided.

In FIG. 3, the hybrid DC transmission equipment includes AC systems 1 and 2, conversion transformers 11 and 21, a forward converter 12, a DC reactor 13, and a DC transmission line 31.
, An inverter 22, a power capacitor 23, and an operation command device 30 for commanding operation of the hybrid DC power transmission facility
0, a control device 100 for the forward converter 12, a control device 200 for the inverse converter 22, and a DC current transformer 101.
, A DC voltage transformer 201 and an AC voltage transformer 240.

The forward converter 12 is for converting an alternating current into a direct current, and is constituted by a separately excited converter.

The inverter 22 is for converting DC to AC, and uses a self-excited converter having a self-extinguishing element.

The DC reactor 13 is for smoothing a DC current, and the DC
Numeral 3 is for smoothing a DC voltage.

The DC transmission line 31 may be omitted or very short in the case of equipment for frequency conversion or in the case of asynchronous interconnection.

The DC current transformer 101 is for detecting a current flowing through the forward converter 12, and the detected current value is taken into the control device 100 to perform constant current control. Used.

The DC voltage transformer 201 is for detecting the DC voltage on the inverter 22 side of the DC power transmission equipment, and the detected voltage value is taken into the control device 200 and is controlled by the constant voltage control. Used to perform

The AC voltage transformer 240 is for detecting the AC voltage on the input side of the separately-excited converter, and is used for the control operation of the control device 200 of the self-excited converter to which the present invention is applied.

The operation command device 300 gives a DC transmission power command value or a DC current command value corresponding thereto to the control device 100.
Give the rated voltage value.

The control device 100 includes a constant current control circuit that controls at least a DC current flowing through the DC power transmission equipment to a specified value. The constant current control circuit uses a DC transmission power command value input from the operation command device 300 or a corresponding DC current command value and a current value taken from the DC current transformer 101 to generate a constant current. Perform control.

The control device 200 includes a constant voltage control circuit for controlling at least the DC voltage of the DC power transmission equipment to a specified value (rated value). The constant voltage control circuit performs constant voltage control using a DC voltage command value input from the operation command device 300 and a voltage value taken from the DC current transformer 201. Further, the control device 200 takes in the AC voltage on the input side of the separately-excited converter, which is detected by the AC voltage transformer 240 and rectified by the rectifier circuit 241 and converted into the magnitude of the AC voltage. Under a predetermined condition, a current control operation is performed instead of the control operation of the constant voltage control circuit. Details of the current control operation will be described later.

The transmission path for transmitting the value of the DC side output voltage of the separately-excited converter to the control device of the self-excited converter includes, for example, an optical fiber cable provided along with the DC transmission line 31, forward conversion equipment and A microwave communication device or the like for communicating the inversion equipment can be used. The signal waveform can be transmitted to the DC transmission line 31 by being superimposed on the DC power.

First, with reference to FIG. 4, a description will be given of a control characteristic of a converter which is conventionally considered with respect to the operation of the above-described hybrid DC power transmission equipment. In FIG. 4, the abscissa indicates the DC current, the ordinate indicates the DC voltage, the thin solid line indicates the control characteristics of the forward converter, and the thick solid line indicates the control characteristics of the inverter. The intersection o indicates the operating point.

As shown in FIG. 4, the forward converter operates with the constant current control ACR at the DC current command value Idp corresponding to the rated DC power, and the inverter converts the rated DC voltage to the command value Vd.
It is operating under constant voltage control AVR2 with dp. The forward converter is also provided with a circuit for performing constant voltage control AVR1 having a command value for Vdpu as a backup.

Further, the inverter includes a constant power control circuit APiR during the operation of the inverter and a constant power control circuit APrR during the operation of the forward converter as a power limiter of the constant voltage control circuit AVR. In such an operation, when an accident occurs in the AC system on the side of the forward converter and the AC voltage decreases, the control characteristic of the forward converter becomes as indicated by a broken line, and there is no intersection with the control characteristic of the inverter. Therefore, the DC current stops flowing, and the DC power transmission stops.

Next, a detailed configuration of the control device 200 (see FIG. 3) for the self-excited converter will be described with reference to FIG.

In FIG. 2, a control device 2 for a self-excited converter
00 denotes a current command value creation circuit 211, a first constant power control circuit 212, a constant voltage control circuit 213, a second constant power control circuit 214, a signal selection circuit 215, and a reactive power control circuit 216. , Active current control circuit 217, reactive current control circuit 218, 2φ / 3φ conversion circuit 219, P
And a WM pulse generation circuit 220.

The current command value generating circuit 211 is provided with a DC voltage command value Vdr from the operation command device 300, an upper limit value Idu of the effective current command value, and a magnitude of the AC voltage of the rectifier circuit 241 (see FIG. 3). An effective current command value corresponding to the magnitude of the AC voltage is created using Vdfr as an input.

The first constant power control circuit 212 controls the active power when the self-excited converter 22 operates in the forward converter to the command value Pdr.

The constant voltage control circuit 213 controls the DC voltage of the self-excited converter 22 to a specified value Vdr.

The second constant power control circuit 214 controls the active power when the self-excited converter 22 performs the inverter operation to the command value Pdi.

The signal selection circuit 215 determines the operating state of the self-excited converter among the outputs of the current command value creation circuit 211, the first constant power control circuit 212, the constant voltage control circuit 213, and the second constant power control circuit. Select the optimal output according to.

The reactive power control circuit 216 controls the reactive power on the AC side of the self-excited converter to become the reactive power command value Qr from the operation command device 300.

The effective current control circuit 217 controls the effective current of the alternating current of the self-excited converter 22 to the effective current command value selected by the signal selection circuit 215.

The reactive current control circuit 218 converts the self-excited converter 22 into a reactive current command value generated by the reactive power control circuit.
The inactive part of the AC current is controlled.

The 2φ / 3φ conversion circuit 219 converts two outputs, an output of the active current control circuit 217 and an output of the reactive current control circuit 218, from a biaxial signal to a three-phase signal.

The PWM pulse generation circuit 220 has 2φ
A pulse signal for controlling the self-excited converter 22 is created from the signal subjected to the / 3φ conversion.

With this configuration, it is possible to control two electric quantities, that is, active power such as DC voltage and reactive power. The details of this control are described in Japanese Patent Application No. 3-142967. Note that the suffix f attached to the input signal of each control circuit block indicates a feedback amount from the DC power transmission equipment, Idf indicates an effective component of the AC side current of the self-excited converter, and Iqf indicates an invalid component. It shows the feedback current value of the component.

Next, referring to FIG.
The operation of 0 will be described. In FIG. 1, a thin solid line indicates a control characteristic of the separately-excited converter of the forward converter, and the control characteristic is the same as that of the conventional converter. The thick solid line indicates the characteristics of the self-excited converter to which the present invention is applied.

The constant voltage control AVR2 operates when the DC current set value is between the lower limit current command value Idl and the upper limit current command value Idu in consideration of a margin across the current command value Idr. In the region equal to or higher than the upper limit current command value Idu, the same constant power control APiR as in the related art operates. On the other hand, when the current command value is equal to or lower than the lower limit current command value Idl, a current characteristic in which the current set value changes according to the DC voltage is provided.

If the difference between Idu and Idr, that is, this is expressed in terms of electric energy, Pu (= Idu × Vdr) and Pr (= Idr)
× Vdr) corresponds to the power margin referred to in the conventional Japanese Patent Application No. 7-265144.

A block for generating a command value having a characteristic of changing the current command value according to the DC voltage is provided by a current command value creation circuit 20.
In step 1, a current command value Idp is created from the DC voltage detection value Vdf, for example, according to the following equation 1.

Idp = (Idl / Vdr) × Vdf (Equation 1) In FIG. 1, the control characteristic of the self-excited converter is such that the lower limit of the voltage is limited, and the constant voltage is flat without passing through the origin. It has a control area. This is because constant voltage control is performed at a minimum voltage required to generate a signal voltage to be output in consideration of a voltage loss in the self-excited converter. This constant voltage control can be realized using a constant voltage control circuit similar to the normal constant voltage control.

For reference, FIG. 5 shows one control block of the control device for the separately-excited converter 12 of the forward converter.

In FIG. 5, the control device includes a constant current control circuit 111, a constant voltage control circuit 112, a margin angle control circuit 113, a signal selection circuit 114, and a phase control circuit 115
And is configured.

The constant current control circuit 111 receives a current command value Idp corresponding to the DC transmission power from the operation command device 300 (see FIG. 3) and controls the current flowing through the converter to a command value.

The constant voltage control circuit 112 is provided with a DC voltage command value Vd from the operation command device 300 (see FIG. 3).
r ′ is input, and the DC output voltage of the separately-excited converter is controlled to a command value.

The margin angle control circuit 113 performs control for always keeping the minimum margin angle of the thyristor of the separately-excited converter 12 at a predetermined value or more.

The signal selection circuit 114 includes a constant current control circuit 111, a constant voltage control circuit 112, and a margin angle control circuit 1.
An optimum output signal is selected from the 13 outputs.

The phase control circuit 115 generates a pulse for controlling the thyristor of the separately-excited converter according to the circuit output selected by the signal selection circuit.

With this circuit configuration, the DC / DC voltage characteristic of the separately-excited converter shown in FIGS. 1, 4, 6 and 7 is realized.

FIG. 6 shows an operating point (o ₁ ) on the control characteristics of the converter when the AC voltage on the side of the forward converter drops. In the conventional control method, the DC current becomes zero and the power transmission stops.However, according to the present invention, a control method of changing the current command value according to the DC voltage is used. DC power transmission can be performed with a DC voltage corresponding to this.

Here, in the above description, the current command value of the self-excited converter when the AC voltage on the side of the forward converter drops is set to a value corresponding to the drop of the DC voltage, so that the characteristics of equation 1 can be obtained. However, as shown in FIG. 7, the characteristic may be such that the DC current is constant with respect to the DC voltage. In implementation, since the current command value Idl of the lower limit is obtained from the operation command device 300 by the current command value creation circuit 201 in FIG. 1, this value may be fixed. That is, Idp = Idl [Pd <Pdl (= Vdr × Idl)] (Expression 2) The detected value of the DC voltage is different from that of the first embodiment in which the current command value is changed depending on the DC voltage. Is not necessary for creating the current command value. For this reason, the current command value creation circuit can have a simple configuration.

As a specific current command value, a value having a margin for avoiding interference of a constant current control circuit between the separately-excited converter and the self-excited converter due to the ripple of current, for example, 10 times of the rated DC current. %, Which may be smaller than the current command value of the separately-excited converter. Of course, other values can be used, or the minimum operating current value can be used.

According to the signals detected by the AC voltage transformer 240 and the rectifier circuit 241, a current command value for the self-excited converter at the other end is generated according to the characteristic diagrams shown in FIGS.

Furthermore, in the above description, a DC power transmission system in which a forward converter is connected to a separately-excited converter and an inverter is connected to a self-excited converter one by one is described. The same concept can be applied to a case where a plurality of devices are connected.

[0062]

According to the present invention, by adding a simple control circuit, a self-excited converter and a separately-excited converter that can perform DC power transmission without stopping even in the event of an AC system failure on the forward converter side are assembled. A hybrid DC power transmission facility configured in combination is obtained.

[Brief description of the drawings]

FIG. 1 is a graph illustrating DC voltage-current characteristics of a separately-excited converter and a self-excited converter, illustrating a control method of a self-excited converter according to the present invention.

FIG. 2 is a block diagram showing a configuration of a control device for a self-excited converter according to the present invention.

FIG. 3 is a block diagram illustrating a configuration of a hybrid DC power transmission facility including a separately-excited converter and a self-excited converter according to the present invention.

FIG. 4 is a graph illustrating DC voltage-current characteristics of a separately-excited converter and a self-excited converter, illustrating a conventional control method in a hybrid DC power transmission facility.

FIG. 5 is a block diagram showing a configuration of a control device of the separately-excited converter.

FIG. 6 is a graph showing an operation at the time of a forward converter-side AC system fault.

FIG. 7 is a graph showing DC voltage-current characteristics of the separately-excited converter and the self-excited converter, showing another control method of the self-excited converter of the present invention.

[Explanation of symbols]

1,2 ... AC system, 11,21 ... Transformer transformer, 12 ...
Forward converter composed of separately-excited converters, 13 DC reactor, 31 DC transmission line, 22 Inverter composed of self-excited converter, 23 Capacitor for power, 300 Operation command device, 100 ... Control device, 101 ... DC current transformer, 200 ... Control device, 201 ... DC voltage transformer, 21
DESCRIPTION OF SYMBOLS 1 ... Current command value creation circuit, 212 ... First constant power control circuit, 213 ... Constant voltage control circuit, 214 ... Second constant power control circuit, 215 ... Signal selection circuit, 216 ... Reactive power control circuit, 217 ... Active current control circuit, 218 ... Reactive current control circuit, 219 ... 2φ / 3φ conversion circuit, 220 ... PWM
Pulse generation circuit, 240 AC voltage transformer, 241 rectifier circuit, 111 constant current control circuit, 112 constant voltage control circuit, 113 margin angle control circuit, 114 signal selection circuit, 115 phase control circuit.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Junichi Miyamoto 4-1 Egasakicho, Tsurumi-ku, Yokohama-shi, Kanagawa Prefecture Inside the Electric Power Research Laboratory, Tokyo Electric Power Company (72) Inventor Shunsuke Tanaka E, Tsurumi-ku, Yokohama-shi, Kanagawa Prefecture 4-1 Kasaki-cho Tokyo Electric Power Company

Claims (10)

[Claims] 1. A control device for a self-excited converter in a DC power transmission facility comprising a separately-excited converter and a self-excited converter connected via a DC circuit, wherein the self-excited converter is controlled at a voltage lower than a rated DC voltage. A control device for a self-excited converter, comprising a current control for setting a DC current of the self-excited converter according to an AC voltage of the converter and controlling the current to the set current value. 2. A control device for a self-excited converter of a DC transmission facility, wherein the self-excited converter and the self-excited converter are connected via a DC circuit. A control device for a self-excited converter, characterized in that the DC current of the self-excited converter changes according to the magnitude of the DC voltage of the converter. 3. The control device for a self-excited converter according to claim 1, wherein the control device for the self-excited converter has a current control characteristic having a command value proportional to the DC voltage at a voltage lower than a rated DC voltage. A control device for a self-excited converter, comprising: 4. The control device for a self-excited converter according to claim 1, wherein the control device for the self-excited converter has a current control characteristic of making a DC current constant at a voltage lower than a rated DC voltage. Characteristic control device of self-excited converter. 5. The control device for a self-excited converter according to claim 1, wherein when the voltage is lower than the rated DC voltage, the self-excited converter switches from the constant voltage control characteristic to the current control characteristic. A control device for a self-excited converter, wherein the current value is switched to a current value which is smaller by an amount having a margin than an operation current value. 6. The control device for a self-excited converter according to claim 1, wherein a constant voltage control characteristic of the self-excited converter is switched from a constant voltage control characteristic to a constant power control characteristic at a voltage higher than a rated DC voltage. And a switching device that switches the power with a power value larger than a driving DC current value (power value) by a power margin. 7. In a DC power transmission facility configured by connecting a separately-excited converter and a self-excited converter via a DC circuit, a detecting unit for detecting an input AC voltage of the separately-excited converter; A DC transmission facility comprising: a transmission line for transmitting a detected voltage value; and the control device for a self-excited converter according to claim 2. 8. A control device for a self-excited converter for converting a DC current transmitted under constant current control into AC, wherein a voltage of the transmitted DC current is equal to or higher than a predetermined threshold value. The input side voltage is controlled at a constant voltage, and when the voltage of the transmitted DC current is less than the threshold, the input side current is controlled to a predetermined current value according to the DC current voltage. Control device for self-excited converter. 9. A hybrid DC power transmission facility in which a separately-excited converter and a self-excited converter are connected via a DC circuit, a detecting unit for detecting power supplied to the separately-excited converter. A transmission path for transmitting the value of the detected power, and if the voltage of the transmitted DC current is equal to or greater than a predetermined threshold, the input side voltage is controlled with a constant voltage, and the transmitted DC current is controlled. When the voltage of the current is less than the threshold value, the control device of the self-excited converter for controlling the input current to a predetermined current value according to the value of the transmitted power, and DC power transmission equipment. 10. A control device for a self-excited converter connected to an operation command device for converting a DC current transmitted under constant current control into AC, wherein a DC voltage command value Vdr from the operation command device is effective. A current command value creating circuit for creating an effective current command value corresponding to a DC voltage by inputting a predetermined upper limit value Idu of the current command value and a DC voltage detection value Vdfr of a DC current to be transmitted; A first constant power control circuit for controlling the active power when the exciter converter operates in the forward converter to a command value Pdr, and a constant voltage control for controlling the DC voltage of the self-excited converter to a specified value Vdr A circuit, a second constant power control circuit for controlling the active power when the self-excited converter performs the inverse converter operation to the command value Pdi, the current command value creation circuit, the first constant power control circuit, Constant voltage control times From among the output of the second constant power control circuit,
A signal selection circuit for selecting an output according to the operation state of the self-excited converter, and a control for controlling the reactive power on the AC side of the self-excited converter to be the reactive power command value Qr from the operation command device. A reactive power control circuit, an active current control circuit for controlling the active component of the alternating current of the self-excited converter to a command value of the active current selected by the signal selection circuit, and a reactive power control circuit instructed. A reactive current control circuit for controlling the reactive component of the alternating current of the self-excited converter to a reactive current command value; an output of the active current control circuit; and an output of the reactive current control circuit. A 2φ / 3φ conversion circuit for converting the signal into a three-phase signal; and a PWM pulse generation circuit for generating a pulse signal for controlling a self-excited converter from the signal converted to the three-phase signal. 1st and 2nd The control device for a self-excited converter, wherein the constant power control circuit sets a small current value in accordance with a drop from a rated value of the DC current.